Add a way to use your own certificate authority file/directory

[cminyard]

Add a way to specify your own CA instead of using the one from the system. Much like the "+tls-ca" option to dig.

[cminyard]

BTW, I know that you can set the SSL_CERT_FILE or SSL_CERT_DIR environment variables on Linux, but that is not as clear or reliable as a direct parameter. The environment variables don't work on MacOS. I don't know if they work on Windows.

So a command line option or configuration file option is still much preferred.